1. Field of the Invention
The present invention relates to an ink jet printing apparatus, and more particularly, to an ink jet printing apparatus provided with an ink jet head including a plurality of nozzles.
2. Discussion of the Related Art
In the ink jet printing apparatus provided in a printer, a facsimile device, a copying machine, etc., an ink drop is ejected from a selected nozzle by driving the energy generating medium of the ink jet head in accordance with the printing data by use of an ink jet head provided with a plurality of nozzles for ejecting ink drops, an ink chamber communicating with the respective nozzles, and energy generating media (energy generating elements) such as electromechanical conversion elements or electrothermal conversion elements for generating energy in order to pressurize ink in the respective ink chambers and thereby eject ink drops from the nozzles.
In the present specification, "to drive the energy generating medium" is also referred to as "to drive the nozzle" or "to drive the channel".
When ejecting an ink drop from a selected or designated nozzle, the meniscus of an adjacent non-ejection nozzle which is at that time prohibited from ejecting an ink drop (called "non-drive nozzle") is put in an unstable state by the mechanical or fluid interference.
As a result, the ink ejection speed Vj and the ink ejection amount Mj vary. In the end, air enters the ink chamber through the nozzle of the non-ejection nozzle. Furthermore, in the case of a "non-drive nozzle" being surrounded by two nozzles on either side of the "non-drive nozzle" which are "ejection nozzles" or "drive nozzles" for ejecting an ink drop, the energy generating medium of the two drive nozzles pressurizes the ink chamber and thereby the nozzle forming member of the non-drive nozzle is slightly pushed up. For this reason, the inner volume of the ink chamber of the non-drive nozzle is slightly increased, and thereby, the ink meniscus of the non-drive nozzle is pulled toward the inside of the non-drive nozzle. If such a phenomenon occurs successively, air is accumulated in the ink chamber of the non-drive nozzle.
When the air is accumulated in the ink chamber of the non-drive nozzle in such a way, even though the ink chamber of the non-drive nozzle is pressurized by the energy generating medium, after the non-drive nozzle has been changed to a drive nozzle, the ink drop may not be ejected. As a result, the image quality is lowered and the printing results deteriorate.
In the prior art, there are many methods of driving ink jet print heads. For instance, as described in the published specification of Japanese Laid-open Patent Publication No. 58-203/1983, an ink jet printing head includes adjacent ink chambers and nozzles. In order to make an ink ejection speed uniform in all cases, when one of the pressure chambers is pressurized to thereby eject an ink drop therefrom, the other adjacent pressure chamber is pressurized to a level such that an ink drop is not ejected.
In another prior art device described in the published specification of Japanese Laid-open Patent Publication No. 6-8428/1994, an ink jet printing apparatus includes a pulse signal outputting medium for outputting signals having different pulse widths in synchronism with the drive signal and a signal selection medium for selecting one signal from the output signals. The ON-OFF state of the piezoelectric element driving medium is changed even in the unsaturated area of the drive signal. As a result, the voltage applied to the piezoelectric element is changed so as to make constant the amount of the ink in each ink drop ejected from the respective nozzles. Such a method of driving is well known.
Furthermore, in the ink jet printing apparatus in which plural signals respectively having different pulse widths in synchronism with the drive signal are output and the applied voltage is changed by selecting one signal from the plural signals and changing the state of the drive media for charging the respective piezoelectric elements from "on" to "off", if the turn-off time of the transistors becomes uneven, the applied voltage also becomes uneven. As a result, the applied voltage cannot be controlled with high precision.